The invention relates to a method for producing a pre-recorded, disk-shaped die. The invention also relates to a pre-recorded, disk-shaped die and to a blank information carrier.
It is already known from analog audio disk engineering to cut information signals into metallic recording media and to cast dies directly from this medium. This method developed by the applicant and known as so-called Direct Metal Mastering (DMM) is characterized by high fidelity of shape in the galvanic duplicating process and that several intermediate stages are dispensed with in producing an audio disc.
Analog sound recording is afflicted with fundamental problems which have largely become controllable due to the development of the art. Digital recording of an information signal with subsequent optical laser-readout has also gained a considerable market share in recent years. In this method, the digital signal is usually recorded onto a recording medium by means of complicated optical and chemical processes. The so-called CD's (compact disks (CD's) copied from this are distinguishable by their good acoustical characteristics and by the fact that they can be scanned by a laser in contactless manner.
Handling a CD is simpler for the consumer than handling a conventional record since the surface of a CD is relatively insensitive. The contactless scanning inherent in laser use provides further advantages.
However, the production of a CD is incomparably more complicated than the production of an analog record. The facilities used in the prior art require the use of "super-clean rooms" so there is no risk of dust particles impairing the production process of a disk in an inadmissible manner. The CD master is usually produced in the following manner: A glass plate polished to a high gloss is first subjected to a visual check and then is cleaned and provided with an adhesive layer. A photoresist layer 0.1.mu. thick is applied to the adhesive layer. This 0.1.mu. of thickness corresponds exactly to the 0.1.mu. depth of the signal track on the finished CD to enable the signal track to be read out by a laser beam. The coated glass plate is then checked again and adjusted. This is followed by the recording of the information signal by laser beam so that the locations of exposure can subsequently be washed out in the developing process. The washing out process is continued under laser beam control until the desired pit structure has been achieved. The developed photoresist layer is subsequently provided with a thin silver layer to enable a carrier material to be galvanized on. After the galvanizing is completed, the glass base and the non-exposed photoresist layer can be removed, making the final die (master) and available which in the conventional manner provide the possibility of copying for further processing in subsequent stages.
The plurality of method steps and the complexity of the facilities for checking the desired signal shape necessitate a costly production method which sensitively responds to disturbances, dust particles in the atmosphere and inaccurate method parameters.